The present invention relates to a positive electrode active material for secondary batteries and a manufacturing method thereof and a nonaqueous electrolytic solution secondary battery, and reproduced electronic functional material and a reproduction method of electronic functional material.
Recently, portable electronic devices, such as note type personal computers, personal digital assistants (PDAs), cellular phones, video cameras and so on, are rapidly spreading. As they spread, for secondary batteries for use in the portable electronic devices, there are strong demands for smaller size, higher capacity, higher cycle life and so on.
As a secondary battery capable of satisfying such demands, there is known a Li ion secondary battery that utilizes a nonaqueous electrolytic solution including, for instance, a Li salt. In the Li-ion secondary battery, a Li containing transition metal composite oxide, such as LiCoO2, LiNiO2, or LiMn2O4, is used as the positive electrode active material. For a negative electrode, carbonaceous material is utilized, and a nonaqueous electrolytic solution, in which a lithium salt, such as LiPF6 or LiBF4, is dissolved in a nonaqueous solvent, is utilized.
The Li ion secondary battery has advantages, in comparison with a secondary battery that uses lithium metal, in that safety thereof is remarkably excellent; a voltage a unit cell is high; and a high energy density may be obtained. From these circumstances, the lithium ion secondary batteries are in heavy usage as a power source of the portable electronic device.
The positive electrode active material, such as LiCoO2 or LiNiO2, is normally obtained by sintering a mixture of cobalt oxide or nickel oxide and lithium carbonate in air at a temperature of substantially 900xc2x0 C. to convert into a composite oxide. The composite oxide obtained through the sintering is milled to a particle diameter of substantially from several micrometers to several tens micrometers, followed by suspending, together with a conductive material and a binder, in an appropriate solvent, thereby slurry is prepared. The slurry is coated on a current collector (metal foil), followed by drying, thereby forming in plate. Thus, a positive electrode is prepared.
However, the lithium ion secondary battery, which uses the existing positive electrode as mentioned above, has a problem in that a voltage drop tends to occur at initial charge, thereby causing a decrease in manufacturing yield and a deterioration of battery performance. Furthermore, as to the decrease in the manufacturing yield, clogging when the positive electrode slurry is coated on the collector and destruction of the collector (metal foil) are also decrease-causing factors.
We studied the aforementioned phenomena and found that powdery metal impurities and agglomerated particles mingled in many cases in the positive electrode active material, which was prepared according to the existing manufacturing method, and these caused problems. Since particles of the metal impurity and the agglomerated particles are only slightly mingled, it is considered that these were overlooked in the existing manufacturing process. Furthermore, sieving is generally used in removing the powdery impurities, but cannot effectively remove particles of the metal impurity and the agglomerated particles, which are small in the difference of particle size from that of particles of original active material.
From these circumstances, in the positive electrode active material for secondary batteries, it is strongly demanded to remove battery performance- and manufacturing yield-deteriorating factors. Furthermore, the impurity particles and agglomerated particles cause problems not only in the ordinary positive electrode active material for secondary batteries, but also in the positive electrode active material, which is physically recovered from waste electrodes and reproduced.
That is, in relation to recent problems of resource starvation and environmental contamination, demands for reproduction of electric appliances are stronger than ever. In electronic functional materials for use in various kinds of electric appliances, in general, expensive metal materials are used. Accordingly, so far, necessity of recovery has been discussed, and recovery and reuse have been actually tried.
In a manufacturing process of secondary batteries, such as lithium ion batteries, due to condition adjustment and cutting into a specified size, there occurs a large amount of waste electrodes, to which the positive electrode active material sticks. From such waste electrodes, Co is recovered and refined by melting; it is once returned to raw material Co3O4 or the like; thereafter, the positive electrode active material is reproduced by synthesizing again LiCoO2 or the like.
The aforementioned method is called a chemical reproduction because the recovered waste material is chemically returned to raw material before synthesis. In this method, since the electronic functional material being reused has to be re-synthesized from raw material, there is a problem in that reproducing costs are high. Meanwhile, it has been studied to reproduce the electronic functional material without performing separation of the raw material and re-synthesis.
As to the waste electrodes of the secondary batteries, a method for directly recovering the active material, such as LiCoO2 or the like, is proposed (Japanese Laid-Open Patent Application No. 10-8150 JP-A). Specifically, an Al foil (waste electrode), on which the positive electrode material is coated, is heat-treated at a temperature where Al is not melted and LiCoO2 is not decomposed. Thereby, the positive electrode material is separated from the Al foil, and the conductive material and binder are decomposed and removed. Thereby, the positive electrode active material, such as LiCoO2 or the like, may be directly recovered.
In order to discriminate such recovery, reproduction method from the chemical reproduction, which chemically converts to the raw material before the synthesis and recovers, this method is called here a physical reproduction method. The physical reproduction method has advantages over the chemical reproduction method in that processing costs for reproducing the electronic functional material are lower; it is very advantageous from a practical point of view.
As a general physical reproduction process, first, powdery, slurry-like, coating-like electronic functional materials, which are target objects, are recovered from various kinds of electronic components and waste materials of the electronic appliances. When the electronic functional material being reproduced is coating-like, it is peeled from a substrate or the like. Then, large foreign material, such as the substrate, from which the electronic functional material has been peeled off, is separated and removed, further followed by removing the foreign material or impurities, which are capable of removing by washing. As needs arise, heat-treatment, acid- or alkali-treatment is applied to remove removable foreign material and impurities. Furthermore, by applying sieving or drying, without performing the synthesis, reproduced powdery electronic functional material is obtained.
In the physical reproduction, it is necessary that characteristics of the electronic functional material is not deteriorated, even after the various kinds of treatment processes are applied. However, there are problems in that due to mingling of the foreign material, which is actually difficult to separate, fine powder caused by brittleness due to heat in the peeling- or heat-treatment process, mingling of large agglomerations due to residuals of the binder component, characteristics of the reproduced electronic functional material deteriorate. In the physical reproduction of the positive electrode active material for secondary batteries, there is a large possibility of mingling of the impurities, which are difficult to separate by means of the sieving or the like, and furthermore there are a lot of agglomerations of the active material. When the secondary batteries are manufactured by use of such reproduced positive electrode active material, there are problems in that the battery characteristics and the manufacturing yield deteriorate.
From these circumstances, it is desired to heighten utility value of the physical reproduction by suppressing the characteristics deterioration of the electronic functional material (reproduced material) obtained by the physical reproduction. The physical reproduction of the electronic functional material is applied not only to the positive electrode active material of the secondary battery, but also to the reuse of phosphor, which is recovered from phosphor slurry used in manufacturing cathode ray tubes or fluorescent lamps. Also in the physical reproduction of the phosphor, the impurity particles and agglomerated particles are the factors that deteriorate the characteristics and the manufacturing yield of the phosphor.
An object of the present invention is to provide a positive electrode active material for secondary batteries, which allows improving the manufacturing yield of the nonaqueous electrolytic solution secondary batteries and attaining an improvement in the battery characteristics, by removing the factors that deteriorate the battery characteristics and the manufacturing yield, and a manufacturing method thereof, and furthermore a nonaqueous electrolytic solution secondary battery that uses such positive electrode active material. Another object of the present invention is to provide a reproduced electronic functional material, of which characteristics deterioration is suppressed by allowing assuredly and industrially separating/removing foreign materials, impurities, fine powders, coarse agglomerations and so on that mingle during the various kinds of recovery and reproduction processes, and a reproduction method of the electronic functional material.
A positive electrode active material of the present invention for secondary batteries comprises a metal oxide powder for use in nonaqueous electrolyte secondary batteries, in which a content of a coarse particle having a particle diameter of 600% or more relative to an average particle diameter of the metal oxide powder is 1 vol. % or less, and a content of a high density particle having a density of 150% or more relative to an average density of the metal oxide powder is 1000 ppm or less by mass.
A positive electrode active material of the present invention for secondary batteries further comprises 1 vol. % or less of a fine particle having a particle diameter of 15% or less relative to the average particle diameter of the metal oxide powder, and 1000 ppm or less by mass of a low density particle having a density of 50% or less relative to the average density of the metal oxide powder.
Another positive electrode active material of the present invention for secondary batteries comprises a metal oxide powder for use in nonaqueous electrolyte secondary batteries, in which a content of a coarse particle having a particle diameter of 30 xcexcm or more is 1 vol. % or less, and a content of a high density particle having a density of 7 g/cm3 or more is 1000 ppm or less by mass.
A positive electrode active material of the present invention for secondary batteries further comprises 1 vol. % or less of a fine particle having a particle diameter of 0.5 xcexcm or less, and 1000 ppm or less by means of a low density particle having a density of 2.5 g/cm3 or less.
A method of manufacturing a positive electrode active material of the present invention or secondary batteries, in manufacturing a powdery positive electrode active material by mixing raw material powders of the positive electrode active material for secondary batteries with a desired ratio and sintering this mixture, by making use of the difference of resistance force due to the particle diameter or the density of the particle constituting the powdery positive electrode active material, the simultaneously separating and removing a coarse particle and a high density article from the powdery positive electrode active material is implemented so that the course particle having a particle diameter of 250% or more relative to an average particle diameter of powdery positive electrode active material and the high density particle having a density of 120% or more relative to an average density of the powdery positive electrode active material, may be simultaneously removed.
In a method of manufacturing a positive electrode active material for secondary batteries of the present invention, a separating and removing process is implemented, for instance, so that a coarser particle having a particle diameter of 250% or more relative to an average particle diameter of powdery positive electrode active material, and a high density particle having a density of 120% or more relative to an average density of the powdery positive electrode active material, maybe simultaneously removed. Furthermore, the separating and removing process is implemented by use of, for instance, a classifier.
A manufacturing method of the present invention of positive electrode active material is implemented, for instance, so that a fine particle having a particle diameter of 50% or less relative to the average particle diameter of the, powdery positive electrode active material, and a low density particle having a density of 75% or less relative to the average density of the powdery positive electrode active material, may be simultaneously removed from the powdery positive electrode active material.
A nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode, which includes a positive electrode active material consisting essentially of a Li containing composite metal oxide power and of which content of a coarse particle having a particle diameter of 600% or more relative to an average particle diameter of the composite metal oxide powder is 1 vol. % or less, and of which content of a high density particle having a density of 150% or more relative to an average density of the composite metal oxide powder is 1000 ppm or less by mass: a negative electrode disposed so as to face, through a separator, the positive electrode: a battery case, which accommodates the positive electrode, the separator, and the negative electrode: and a nonaqueous electrolytic solution filled in the battery case.
Another nonaqueous electrolytic solution secondary battery of the present invention comprises a positive electrode, which includes a positive electrode active material consisting essentially of a Li containing composite metal oxide powder and of which content of a coarser particle having a particle diameter of 30 xcexcm or more is 1 vol. % or less, and of which content of a high density particle having a density of 7 g/cm3 or more is 1000 ppm or less by mass: a negative electrode disposed so as to face, through a separator, the positive electrode: a battery case, which accommodates the positive electrode, the separator, and the negative electrode: and a nonaqueous electrolytic solution filled in the battery case.
As mentioned above, there are mingled powdery metal impurities and agglomerated particles in the positive electrode active material for secondary batteries, and these may cause problems. In particular, higher density particles, such as powdery metal impurities large in particle size, elute due to a high positive electrode potential at the initial charge of the secondary battery, and eluted metal ions are reduced at the negative electrode side and precipitate there. Thereby, a micro-short circuit may be caused. In addition, the coarser particles, such as the agglomerated particles, may remain between a coating bed and a substrate at the coating of the positive electrode, or may cause destruction in a metal foil, a current collector. Furthermore, the finer particles and the lower density particles may be factors that deteriorate the battery characteristics.
As a method for removing the coarser and finer particles, the sieving (wet or dry method) is generally used. However, since the positive electrode active material has a small particle size in the range of from several micrometers to several tens micrometers, the dry sieving immediately causes the clogging of the sieve. Accordingly, the dry sieving method is substantially impossible to put into practical use. While, according to the wet sieving, the clogging problem may be solved, since the particle size difference between the coarser particles, such as the agglomerated particles, and the original positive electrode active material is small, an ordinary wet sieving may not allow obtaining sufficient separation accuracy. In addition, the sieving may not remove powdery metal impurities or the like.
In the present invention, by making use of the difference of resistance force due to the sizes and the densities of the particles constituting the positive electrode active material for secondary batteries, the coarser particles and the higher density particles are simultaneously separated and removed from the positive electrode active material. This separating/removing process may further allow separating/removing the finer particles and the lower density particles. That is, resistance force of the particle against physical force, such as gravitational force, inertial force, centrifugal force and so on of the particle differs due to the particle size and the density thereof. Accordingly, by making use of the difference of such resistance force, the coarser particles and the higher density particles, and furthermore the finer particles and the lower density particles, may be easily separated and removed with accuracy.
The aforementioned separating/removing process may be implemented by use of various kinds of classifiers. For instance, in a dry centrifugal classifier, classification points may be set finely divided based on the particle size and the density of the particle. Accordingly, even the coarser particles, such as the agglomerated particles, which is small in the particle size difference from the positive electrode active material for secondary batteries, and the higher density particles, such as the powdery metal impurities may be separated and removed with high accuracy. Furthermore, the finer particles and the lower density particles may be similarly separated/removed with high accuracy.
By carrying out the aforementioned separating/removing process, the positive electrode active material for secondary batteries, of which contents of the coarser particles and the higher density particles are simultaneously reduced, may be obtained with high reproducibility. By use of such positive electrode active material for secondary batteries, the micro-short circuit of the secondary battery due to such higher density particles and coating failure during positive electrode manufacture due to the coarser particles may be suppressed from occurring. Accordingly, the secondary batteries excellent in the battery characteristics and high in the manufacturing yield may be provided.
Furthermore, even when the electronic functional material is reproduced by means of the physical reproduction, the foreign material, impurities, the coarser particles, such as the agglomerated particles, or the higher density particles mingle during the recovering and reproducing process. These cause the deterioration of the characteristics of the reproduced electronic functional material. Even for the removal of such coarser particles and the higher density particles, and in addition, the finer particles and the lower density particles, which mingle in the reproduced electronic functional material, the aforementioned separation and removing process, which make use of the difference of the resistance force due to the particle sizes and the densities of the particles, may be effective. In the reproduced electronic functional material of the present invention and the reproduction method of the present invention of the electronic functional material, such separating and removing process is applied.
That is, the reproduced electronic functional material of the present invention is the reproduced powdery electronic functional material recovered and reproduced from waste electronic components or waste material produced in the manufacturing process of the electronic components; the reproduced powdery electronic functional material contains 1% or less by volume of coarser particles, of which particle sizes are 600% or more with respect to an average particle size of the powder, and 1000 ppm or less by mass of higher density particles, of which densities are 150% or more with respect to an average density of the powder.
The reproduced electronic functional material of the present invention includes 1% or less by volume of finer particles, of which particle sizes are 15% or less with respect to the average particle size of the powder, and 1000 ppm or less by mass of lower density particles, of which densities are 50% or less with respect to the average density of the powder.
Another reproduced electronic functional material of the present invention is reproduced powdery electronic functional material recovered and reproduced from waste electronic components or waste material produced in the manufacturing process of the electronic components; the reproduced powdery electronic functional material contains 1% or less by volume of finer particles, of which particle sizes are 15% or less with respect to the average particle size of the powder, and 1000 ppm or less by mass of lower density particles, of which densities are 50% or less with respect to the average density of the powder.
A reproducing method of electronic functional material of the present invention includes recovering the electronic functional material from waste electronic components or waste material produced in the course of manufacturing the electronic components; and reproducing the powdery electronic functional material by refining the recovered electronic functional material; wherein in the course of refining the recovered electronic functional material, by making use of the difference of the resistance force due to the particle sizes and the densities of the particles constituting the powdery electronic functional material, the simultaneously separating and removing the coarser particles and the higher density particles from the powdery electronic functional material is implemented so that the coarser particles, of which particle sizes are 250% or more with respect to an average particle size of powdery electronic functional material, and higher density particles, of which densities are 120% or more with respect to an average density of the powdery electronic functional material may be simultaneously removed.
In the reproduction method of the electronic functional material of the present invention, the separating/removing process is performed, for instance, so that the coarser particles, of which particle sizes are 250% or more with respect to an average particle size of powdery electronic functional material, and higher density particles, of which densities are 120% or more with respect to an average density of the powdery electronic functional material may be simultaneously removed. Furthermore, the separating/removing process may be performed by means of, for instance, the classifier.
In the reproduction method of the present invention of the electronic functional material, the separating/removing process is performed further so that the finer particles, of which particle sizes are 50% or less with respect to an average particle size of the powdery electronic functional material, and the lower density particles of which densities are 75% or less with respect to an average density of the powdery electronic functional material may be simultaneously removed from the powdery electronic functional material.
Another reproducing method of the present invention of electronic functional material includes recovering the electronic functional material from waste electronic components or waste material produced in the course of manufacture of the electronic components: and reproducing the powdery electronic functional material, the coarser particles and the higher density particles are simultaneously separated and removed from the powdery electronic functional material.